Stabilized rubber adhesive



Patented Oct. 21, 1952 UNITED sures PATENT OFFICE STABILIZED RUBBER ADHESIVE Cyrus'WlBemmels, New Brunswick, N. 3., assignor to-Industria'l Tape Corporation, a corporation o'f New-Jersey --No Drawing. Application July 7, 1949,

Serial No. 103,540

ii 40laims. (CL 260755) compositions of the type ofxmechanical rubber oods. is relatively soft prior to and during actual use and undergoesislight vulcanization or cure only in rare cases. The .usual soft rubber .compound is as soft and soluble asthe rubber upon which it is based and normally even softer and more soluble.

Compounds .of this nature are subject to oxidation and other deteriorating influences. -In the course of this oxidation the compound softens substantially'at first, i. e., in the first few weeks or months .of aging,..and .hardens thereafter progressively, soon reaching the point where. the softness and tack. required in adhesives and similar compounds are totally absent'and where the .end productbeoomes useless. Some 28X- tension of the useful'life'of soft rubber compoundsls obtained with the rubber antioxidants of the prior art.'but this'improvement is much less pronounced in soft and soluble-compounds than in the 'case'ofso-called mechanical rubber compounds which are substantially vulcanized. After such vulcanization, perhaps due to their tightly bonded, insoluble state, vulcanized mechanical rubber compounds appear substantially stabilized against most oxidative influences, if standard rubber antioxidants of the prior art-are incorporated. The soft rubber compounds -on the other hand remain soluble (for instance inaliphatic solvents such as normal heptane reactive, and accordingly subject to oxidation prior to-and during use. In-some cases soft rubber compounds lose all of their valuable properties between the timethat they are made. and first tested and the time at which they are to be used, sometimes in afew weeks.

This invention is based onthe discoverythat oxidation of the above described soft rubber compounds may be substantially prevented by. a.ddi-. tion thereto of certain metal dithiocarbamates.

in the past as accelerators in the su lphur vulcanization of hard rubber compounds, but; due tothe fact that sulphur vulcanization-appears to inhibit oxidation substantially when normal antioxidants such as the ones ofthe prior art are present, the oxidation inhibiting properties of these metal dithiocarbamates were not utilized in such vulcanized compounds.

In accordance with the present invention some metal dithiocarbamates are used in substantially uncured and accordingly soluble rubber compositions which are substantially uncurable as no amount of sulphur or other sulphur bearing curing agents that would cause curing or in- .solubility are present. The invention involves the incorporation. of preferably from about 0.3

:to about ten per cent of a metal dithiocarbamate in soft and insoluble rubber compounds that are both substantially uncured and substantially uncurable.

Apparently the dithiocarbamates act in soluble soft rubber compounds of thistype to prevent oxidation of the rubber substantially without curing or vulcanizing the rubber. Were the softrubber-compound vulcanized by the action of. the dithiocarbamates, the tackiness of the compounds and many other valuable properties at a relatively low vulcanization stage after somewhat less cure than is required to make a satisfactory vulcanized product such as a tire, a hot water bottle, rubber tubing, and the like.

The dithiocarbamates of antimony, bismuth,

cadmium, copper, lead, selenium, sodium, tin,

and zinc are most satisfactory in inhibiting oxi- "-dithiocarbamate group of thisformula may be Some metal dithiocarbamates have been used dation of soft and soluble rubbercompounds. "The formula of such a metal dithiocarbamate may be represented by For satisfactory oxidation resistance .R .inany any alkyl '(including aralkyl), aryl (including alkaryl), or alkamine group. R can be hydrogen or any alkyl (including aralkyl) or alkamine group. Me may be any of the above mentioned metals. n equals the valence of the metal. R and R groups having from 1 to 11 carbon atoms are preferred, although some inhibition of oxidation is encountered even in dithiocarbomates having very long chain carbon radicals. In polyvalent metal dithiocarbamates the individual dithiocarbamate radicals may differ from each other. Best activity is encountered with dithiocarbamates wherein R and R each are saturated and include 2 to 9 carbons, preferably as aliphatic chains. While the inhibiting effect does not decrease substantially on a molar basis in compounds wherein R and/r R contain more than 4 carbons, the inhibiting effect is somewhat lower in a direct weight comparison apparently because the number of active molecules the invention by Way of example only, but not to limit the scope of the invention in any way, several examples of preferred embodiments are described. The amount of ingredients in all of these examples are given as parts by weight.

The above ingredients are incorporated on a rubber mill in the usual manner until a homogeneous becomes less as the substituted radical becomes 1 Of course, more than one dithiocaan. blend is obtained. Alternatively the ingredients bamate may be present in any one soft rubber y b ed i a er er a r D ecompound. liminary milling of the rubber to cause them The soft and soluble rubber compounds that t blend m ye Soft d Soluble are commercially most satisfactory contain from rubber C p forms a Sa y normally abo t n t abo t three per nt by eight; of tacky and pressure sensitive adhesive mass and the total compound of dithiocarbamate, although has a considerably more uniform useful life than benefits are obtained using lower amounts. corresponding products comprising either no anti- Amounts higher than three per cent are desiroxidant whatsoever or only standard antioxidants able in some cases, e. g. where maximum insurof the prior art. ance against oxidation is desired, or where very Several other examples using widely varied high molecular weight dithiocarbamates are used. dithiocarbamates and other ingredients are illus- To illustrate representative embodiments of trated in the table that follows:

Example No. II III IV V VI VII VIII IX1 X9 XI XII XIII XIV XV Ingredient of Formulae:

Balata, Chilte Balata, Massaru. Balata, Venezuelan Butadieno (76%)-Styrene (24%) Copolymer,

Mooney Value 66 Polyisobutylene (Molecular Weight 80,000-

120,000) Rubber, Natural, Raw.. Rubber, Reclaim Devulcamzed Iaratcrtiary Amyl Phenol Formaldehyde,

soluble and reactive (melting point. 85 0.). Polybetapinene (melting point, 70 C.) Polybetapinene (melting point. 115 C.) Rosgn Dehydrogenatcd (melting point,

Rosin, Gum (melting point, C.) Rosin, Hydrogenated (melting point, 76 0.). Rosin, Hydrogenated, Glyeeride (melting point, 80 C.)

Oil, Mineral Paraffin Wax (melting point, 165 C.)

Calcium Carbonate Titanium Dioxide Zinc Oxide Paratertiary Amyl Polyhydroxyphenol (melting point, C.) Phenyl-beta-Naphtylamine Antimony Dibutyl Dithiocarbamate. Bismuth Diethyl Dithiocarbamate Bismuth Dimethyl Dithiocarbamate. Cadmium Dibutyl Dithiocarbamata. Copper Dimethyl Dithiocarbamate Lead Dimethyl Dithiocarbamate. Selenium Dibutyl Dithiocarbamate. Selenium Dietbyl Dithiocarbamate. Sodium Dibutyl Dithiocarbamate Tin Dibutyl Dithiocarbamate Zinc Butyl Dithiocarbamate.

Zinc Dibutyl Dithiocarbamate. Zinc Diethyl Dithiocarbamate.. Zinc Diethylenetriamine Dithioearbamate Zinc Diisoamyl Dithiocarbamate Zinc Diisopropyl Dithiocarbamate Zinc Dimethyl Dithiocarbamate Zinc Dioctyl Dithiocarbamate Zine (Orthotolylaminoethyl) Orthotolyl Dimethyl Dithiocarbamate Zinc Octadecyl Dithiocarbamate Zinc n-Pentamethylene Dithiocarbamate Zinc Phenyl Ethyl Dithiocarbamate Example N0. XVI XVIII XIX XX XXI XXII XXV XXVI XXVII XXVIII XXIX Ingredient of Formulae:

Balata, Chilton Balata, Massara Balata, Venzuelan Butadiene (76%)-Styrene (24%) Copolymer, Mooney Value 66.... Polyisobutylene (Molecular Weight 80,000l20,000) Rubber, Natural, Raw i. Rubber, Reclaim Devulcanized k Paratertiary Amyl 'Ihenol Formaldehyde, soluble and reactive (melting point 85 C.) 0, Polybetapinene (melting point,

point, C Polybetapinene- (melting point,

Rosin. Dehydrogenated (melting point, C.) Rosin, Gum (melting point, C.) Rosin, Hydrogenated (melting point, 76 C. Rosin, Hydrogenated, Glyoeride (melting point, 80 C.) Lanolin Oil, Mineral Parraifin Wax (melting point,

Calcium Carbonate Cla Zinc Oxide Paratertiary Amyl Polyhydroxy- 1 phenol (melting point, 150 C.) Phen Lbeta-NaphtyIamine Antimony Dibutyl Dithioearbamate Bismuth Diethyl Dithiocarba-- mate Cadmium Dibutyl mate Copper Dimethyl mate H. Lead Dimethyl Dithio b Selenium Dibutyl Dithiocarbamate Selenium Diethyl Dithiocarbamate Sodium Dibutyl Dithiocarbamater Tin Dibutyl Dithiocarbamate- Zine Butyl Dithiocarbamate Zinc Diamyl Dithioearbamate Zinc Dibenzyl Dithiooarbarnate. Zine Dibutyl Dithiocarbamate Zinc Diethyl Dithiocarbamate Zinc Diethylenetriamine Dithiocarbamate .l Zinc Diisoamyl Dithiocarbamate Zinc Diisopropyl Dithiocarbamate. Zinc Dimethyl Dithiocarbamate. Zinc Dioctyl Dithiocarbamate Zinc (Orthotolylaminoethyl) Orthotolyl Dimethyl Dithiocarbamate Zinc Octadecyl Dithiocarbamate. Zinc n-Pentamethylene Dithiocarbamata; Zinc Phenyl Ethyl Dithiocarbamate;

1 A heat sealing adhesive composition. Z A shoemakers cement; may be applied from toluol solution.

Parts Rubber, raw, natural 33 Rosin, dehydrogenated 28.6 Starch 8.8 Lanolin 7.2 Titanium dioxide 8.8 Zinc oxide 13.6 Stabilizer 3 This composition was processed in the'same manner as Example I and then placed in an oxy enbomb to determine its behavior under, strong oxidizin influences.

In another test transparent soft rubber masses of the following formula were thinly spread ona cellophane film backing, and pressed against thin {00nd paper, then irradiated under a 450 watt sunamp:

Rubber parts Rosin glyceride (as in examples) 31 parts Polybetapinene (melting point,

C.) 31 parts Paratertiary amylphenol formaldehyde 55 parts Paratertiary hydroxy phenol" 2.75 parts Stabilizers of the invention 0.001 mol per 20 grams of the above composition It was noted that under the influence of ultraviolet rays masses free of the stabilizers of the invention decomposed readily to a semi-fluid state and penetrated the paper while stabilized soft rubber compounds would remain in their original physical condition and did not flow. The degree of penetration of bond paper after seventy-two hours was measured in the case of many compositions. The results of these tests are summarized in the following table:

Performance Performance Stabilizers Evaluated in Oxygen in ltra- Bomb violet Tests Antimony Dibutyl Dithiocarbamate. Good Bismuth Dimethyl Dithiocarbamata... .do

Cadmium Dibutyl Dithiocarbamate. Superior.

Copper Dimethyl Dithiocarbamate. Good Very Good. Lead Dimethyl Dithiocarbamate Very Good. Do.

Lead (rtl1otolylaminoethyl) Orthotolyl Good Dimethyl Dithiocarbamate. Zinc (Orthotolylaminoethyl) Orthotolyl Dimethyl Dithiocarbamate. Selenium Dimethyl Dithiocsrhamate. Selenium Diethyl Dithiocarbamate.

Tin Dibutyl Dithiocarbamate (St-aim Zinc Butyl Dithiocarbamate Zinc Di-n-Amyl Dithiocarbamate Zince Dibenzyl Dlthiocarbamate Very Good. Superior. Zinc Di-n-butyl Dithiocarbamate. Supcrior Do. Zinc Dicetyl Dithiocarbamate Good Zinc Diethylene Triamine Dithiocar- Superlor bamate. Zinc Diethyl Dithiocarbamate do Superior. Zinc Diisoamyl Dithiocarbamate. do o. Zinc Diisopropyl Dithiocarbamate .do Zinc Dimethyl Dithiocarbamate Very Good Superior. Zinc Di-n-octyl Dithiocarbamate Superior.. Do. Zinc Octadecyl Dithiocarbamate Good Zinc n-Pentamethylene Dithiocarbnm- ...do Superior ate. Non or only Prior Art Antioxidant Bad Bad.

In the above table performance in the oxygen bomb was rated as follows:

Bad-If the compound softened within 24 hours.

Good-If the compound withstood at least 24 hours of test without softening.

Very GoodIf the compound withstood at least 96 hours of the test without softening.

Superior-If the compound withstood at least 144 hours of the test without softening.

Experience shows that compounds containing only prior art anti-oxidants did not withstand 24 hours of the test.

Performance in the ultraviolet test was rated as follows:

Bad-If there was bad penetration so as to transparentise the paper.

Good-If there was only moderate penetration of the bond paper.

Very Good-If there was only slight penetration of the bond paper.

SuperiorIf there was no penetration of the bond paper.

As many of the compounds listed in the preceding examples are typical normally tacky and pressure-sensitive adhesives, it should be mentioned here that such adhesives may comprise 25-90 per cent by weight of at least one rubber, which may be natural or synthetic, 0-70 per cent of at least one tackifying or other compatible resin, 0-40 per cent liquid or waxy plasticizer material, 0-80 per cent filler material, and 0-10 per cent of any standard antioxidant other than of the type of the invention. For best adhesiveness the corresponding limits are 25-75 per cent of rubber material, 10-50 per cent tackifying resin material, 0-20 per cent liquid or waxy plasticizer material, 0-50 per cent filler material, and 0-5 per cent standard antioxidant.

The invention is, of course, suitable for use in soft and soluble rubber compounds other than pressure-sensitive adhesives and some examples of such compounds were listed. Other uses of the invention in soft rubber compounds and many other variations of the above described invention will be apparent to those skilled in the art and are included in the inventive concept.

I claim:

1. A substantially uncurable, dry and normally tacky composition consisting essentially of approximately 33 per cent natural rubber in its soft, soluble and substantially unvulcanized state, approximately 28 per cent rosin, filler and, as a stabilizer. from about one to about three per cent by weight of the composition of at least one zinc dialkyl dithiocarbamate having from one to ten carbon atoms in each alkyl group.

2. A substantially uncurable, dry and normally tacky composition consisting essentially of from about thirty two per cent to about sixty per cent of natural rubber in its soft, soluble and substantially unvulcanized state, from about twentyone per cent to about forty-one per cent of a tacky resin compatible therewith, filler, and, as a stabilizer, from about one to about three per cent by weight of the composition of at least one zinc dialkyl dithiocarbamate having from one to ten carbon atoms in each alkyl group.

3. A substantially uncurable, dry and normally tacky composition consisting essentially of from about thirty-two per cent to about sixty per cent of rubber in its soft. soluble and substantially unvulcanized state, from about twenty-one per cent to about forty-one per cent of a tacky resin compatible therewith, and, as a stabilizer, from about .03 to about ten per cent by weight of the composition of at least one dithiocarbamate of the formula:

wherein R is at least one member of the group consisting of saturated and unsaturated alkyl, aryl and amino-substituted alkyl and aryl groups; R is at least one member of the group consisting of hydrogen and any alkyl, and amino-substituted alkyl group; Me is a member of the group consisting of antimony, bismuth, cadmium, copper, lead, selenium, sodium, tin and zinc; and n equals the valence of the metal.

4. A composition in accordance with claim 3 wherein the dithiocarbamate is a zinc dithiocarbamate comprising a cyclic radical with from four to nine carbon atoms.

CYRUS W. BEMMELS.

(References on following page) 9 REFERENCES CITED i ggg g The following references are of record in the gi egjgqg file of this patent: 2,319,959

UNITED STATES PATENTS 5 Number Name Date Number 1,386,153 Bruni 2, 1921 316,692 1,499,752 Russell y 1, 1924 368,509

10 Name Date Krogh Aug. 22, 1933 Cohen Aug. 8, 1939 Tierney May 25, 1943 FOREIGN PATENTS Country Date Great Britain Aug. 8, 1929 Great Britain Mar. 10, 1932 

1. A SUBSTANTIALLY UNCURABLE, DRY AND NORMALLY TACKY COMPOSITION CONSISTING ESSENTIALLY OF APPROXIMATELY 33 PER CENT NATURAL RUBBER IN ITS SOFT, SOLUBLE AND SUBSTANTIALLY UNVULCANIZED STATE, APPROXIMATELY 28 PER CENT ROSIN, FILLER AND, AS A STABILIZER, FROM ABOUT ONE TO ABOUT THREE PER CENT BY WEIGHT OF THE COMPOSITION OF AT LEAST ONE ZINC DIALKYL DITHIOCARBAMATE HAVING FROM ONE TO TEN CARBON ATOMS IN EACH ALKYL GROUP. 